a Parmer, The Maryland YVellow-throat. 229 
more extensive yellow of the underparts and dorsum. ‘The type 
has a wing formula of 4-3-5—2-6-—1-—7-—8, with the widest space 
between the 5th and 6th. The 6th is of course more worn. 
Except in formosa the females of all the forms are quite differ- 
ent from the males in coloration. ‘The presence of an interrupted 
eyering in the females of the f#zchas group is also found in the 
males of some of the agz/is and foliocephala groups, an evidence of 
their incomplete or imperfect evolution. This eyering is absent 
or slight in the more tropical forms. Its occurrence in young 
males indicates a step in their evolutional change from the an- 
_cestral form. 
In melanops we have an approach to the Mexican and Central 
American species in which the ashy crown band is absent and re- 
placed by a yellow band or by the green of the dorsum. It is 
truly an intermediate between the highly specialized ¢v1chas type 
and the lower but more brilliant swéfava type, the transition oc- 
curring on the one hand through /lavovelata and batrdi and on 
the other through occzdentalis and perhaps roscoe. Beldingi is an- 
other extreme of the #avovelata and flaviceps type. 
The differences here presented are zoégeographical. As the 
food of males and females is probably similar we have no clue 
there to the causes that have brought about such a. contrast 
between the sexes. Why then have they differed and why in 
Jormosa are they so alike? /vrmosa differs from the others in 
the character of the songs of the males. It is a simple warble, 
not the outpouring burst of the f77chas type. The vivacity and 
more active life of the males of this last species and their great 
song powers have seemingly led to an accentuation of pigment 
on the forward part of the body. It would seem that there is 
some element in their food taken in the damp shady retreats of 
their habitats which in combination with their active, songful life 
has permitted this accentuation of pigment. Natural selection 
by permitting, as a rule, the most striking and hence the most 
active and enduring, to propagate, not by any selective ability of 
the females, but by the greater vigor and persistence of the 
males, has slowly evolved the strong characters of the males. 
Boreal influences and a long migration have prevented the agi/s 
group from progressing to the same extent as in frichas. 
